Rx overruns on vortex 3com card ...possible causes??

Hi I have a unit running in production whose primary lan interface eth0 
is a vortex based 3com card.

The system itself is redhat with 2.4.18-27.7.xsmp kernel running on a 
single processor pentium3 SBC

the foolowing stats are seen after reboot:
uptime of
  10:48pm  up  5:43,  1 user,  load average: 0.00, 0.03, 0.00

The card is receiveing many overruns on its Rx buffers:. while this does 
not seem to affect functioning i am afraid of what impact it may have 
during a critical production day.

  ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:00:D5:5D:5F:60
           inet addr:10.88.88.1  Bcast:10.88.88.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:341811 errors:0 dropped:0 overruns:5350 frame:0
           TX packets:280894 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:305966651 (291.7 Mb)  TX bytes:33789603 (32.2 Mb)
           Interrupt:12 Base address:0xc00


ifconfig five seconds later:

  ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:00:D5:5D:5F:60
           inet addr:10.88.88.1  Bcast:10.88.88.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:342665 errors:0 dropped:0 overruns:5360 frame:0
           TX packets:281600 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:306798608 (292.5 Mb)  TX bytes:33875056 (32.3 Mb)
           Interrupt:12 Base address:0xc000





I know it is not speed and duplexing issues  because of mii-tool output:


  mii-tool eth0
eth0: negotiated 100baseTx-FD, link ok


as well as vortex-diag:

/vortex-diag -a

vortex-diag.c:v2.14 12/28/2002 Donald Becker ([email protected])
  http://www.scyld.com/diag/index.html
Index #1: Found a 3c905C Tornado 100baseTx adapter at 0xc000.
  Station address 00:00:d5:5d:5f:60.
   Receive mode is 0x07: Normal unicast and all multicast.
The Vortex chip may be active, so FIFO registers will not be read.
To see all register values use the '-f' flag.
Initial window 4, registers values by window:
   Window 0: 0000 0000 0000 0000 adad 00bf ffff 0000.
   Window 1: FIFO FIFO 0700 0000 0000 007f 0000 2000.
   Window 2: 0000 5dd5 605f 0000 0000 0000 0052 4000.
   Window 3: 0000 0180 05ea 0020 000a 0800 0800 6000.
   Window 4: 0000 0000 8000 0ccc 0001 8880 0100 8000.
   Window 5: 1ffc 0000 0000 0600 0807 06ce 06c6 a000.
   Window 6: 0000 0000 0000 0500 0000 013a 011c c000.
   Window 7: 0000 0000 0000 0000 0000 0000 0000 e000.
Vortex chip registers at 0xc000
   0xC010: **FIFO** 00000000 00000012 *STATUS*
   0xC020: 00000020 00000000 00080000 00000004
   0xC030: 00000000 eda01260 019d8090 00080004
   0xC040: 00765e5e 00000000 000000b7 00000000
   0xC050: 00000000 00000000 00000000 00000000
   0xC060: 00000000 00000000 00000000 00000000
   0xC070: 00009000 00000000 01600080 00000000
   DMA control register is 00000020.
    Tx list starts at 00000000.
    Tx FIFO thresholds: min. burst 256 bytes, priority with 128 bytes to 
empty.
    Rx FIFO thresholds: min. burst 256 bytes, priority with 128 bytes to 
full.
    Poll period Tx 00 ns.,  Rx 0 ns.
    Maximum burst recorded Tx 128,  Rx 352.
  Indication enable is 06c6, interrupt enable is 06ce.
  No interrupt sources are pending.
  Transceiver/media interfaces available:  100baseTx 10baseT.
Transceiver type in use:  Autonegotiate.
  MAC settings: full-duplex.
  Station address set to 00:00:d5:5d:5f:60.
  Configuration options 0052.



I have done some packet dumps which are available should anyone need the 
info, i was thinking that the errors may have to do with the specially 
written applications that are run in this environment on windows servers 
  which have thier MTU set over 1500 < i dont recall what  but it was 
somewhere in tehe 2800 range? i will have to check

The switch does not seem to complain at all.




Any ideas on how i can stop , prevent, or alleviate this issue of Rx 
overruns?



-- 
Madhav Diwan


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